Co-effects of bedding planes and parallel flaws on fracture evolution in anisotropic rocks

•We performed laboratory experiments on anisotropic analogue rocks containing bedding planes and parallel structural flaws.•Co-effects of bedding planes and parallel flaws on rock rupture and fracture coalescence are elucidated.•Experimental results are implied for field occurrences. Mechanical and fracturing behaviors of natural rocks largely depend on the pattern of major discontinuities. The focus of this study is to elucidate the co-effects of the bedding planes and parallel structural flaws on the rock rupture and fracture coalescence. Uniaxial compression tests are conducted on the analogue rock specimens with various combinations of bedding inclinations (from 0° to 90°), bridge angles (-45°, 0° and 45°) and flaw directions (pro-dip and anti-dip). By analyzing the stress-strain curves and the fracture images recorded throughout the test processes, three stress-strain relationship types, six fracture arrays and seven coalescence categories of the structurally anisotropic rocks are generalized. The experimental results show that mechanical parameters, fracture propagation and fracture coalescence are significantly influenced by the arrangement of bedding planes and flaws. The occurrences of the different fracture arrays are also illustrated from the perspective of mechanisms. A careful comparison of the experimentally observed fracture arrays with field examples shows good applicability of the laboratory experiment to the practice. Stress states in the bridge areas are depicted, which account for the macroscopic coalescence patterns. The different coalescence behaviors resulting from the interplay of bedding planes and structural flaws have implications to the faulting process in bedded strata.